<!DOCTYPE html>
<html lang="ch">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>变量</title>
  </head>
  <body>
    <h1><strong>变量演示</strong></h1>
    <script>
      var a = 123;
      document.write(a);
      window.alert(a);
    </script>
  </body>
</html>
